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Subject: Re: [PATCH] pstore: Refactor compression initialization
To:     Kees Cook <keescook@chromium.org>,
        Joel Fernandes <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org
References: <20181017214124.GA8239@beast>
 <20181018013001.GA99677@joelaf.mtv.corp.google.com>
From:   Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Message-ID: <9ebe40c0-5acc-70e1-587d-ba3f0edf2e7b@codeaurora.org>
Date:   Thu, 18 Oct 2018 10:12:03 +0530
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On 10/18/2018 7:00 AM, Joel Fernandes wrote:
On Wed, Oct 17, 2018 at 02:41:24PM -0700, Kees Cook wrote:
>> With compression initialization now separated from pstore_register(),
>> there is no longer a good reason to do compression method selection
>> during fs init. Instead, merge everything together into the late init.
>> Additionally cleans up the reporting to be more clear.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>> ---
>> This patch goes on top of Joel's. I'll have both in linux-next shortly...
>> ---
>>   fs/pstore/inode.c    |  2 --
>>   fs/pstore/internal.h |  3 --
>>   fs/pstore/platform.c | 65 ++++++++++++++++++++++++++++----------------
>>   3 files changed, 41 insertions(+), 29 deletions(-)
>>
>> diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
>> index 5fcb845b9fec..d814723fb27d 100644
>> --- a/fs/pstore/inode.c
>> +++ b/fs/pstore/inode.c
>> @@ -486,8 +486,6 @@ static int __init init_pstore_fs(void)
>>   {
>>   	int err;
>>   
>> -	pstore_choose_compression();
>> -
>>   	/* Create a convenient mount point for people to access pstore */
>>   	err = sysfs_create_mount_point(fs_kobj, "pstore");
>>   	if (err)
>> diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
>> index fb767e28aeb2..c029314478fa 100644
>> --- a/fs/pstore/internal.h
>> +++ b/fs/pstore/internal.h
>> @@ -37,7 +37,4 @@ extern bool	pstore_is_mounted(void);
>>   extern void	pstore_record_init(struct pstore_record *record,
>>   				   struct pstore_info *psi);
>>   
>> -/* Called during module_init() */
>> -extern void __init pstore_choose_compression(void);
>> -
>>   #endif
>> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
>> index f09066db2d4d..e4737a5fa68c 100644
>> --- a/fs/pstore/platform.c
>> +++ b/fs/pstore/platform.c
>> @@ -274,36 +274,56 @@ static int pstore_decompress(void *in, void *out,
>>   
>>   static void allocate_buf_for_compression(void)
>>   {
>> +	struct crypto_comp *ctx;
>> +	int size;
>> +	char *buf;
>> +
>> +	/* Skip if not built-in or compression backend not selected yet. */
>>   	if (!IS_ENABLED(CONFIG_PSTORE_COMPRESS) || !zbackend)
>>   		return;
>>   
>> +	/* Skip if no pstore backend yet or compression init already done. */
>> +	if (!psinfo || tfm)
>> +		return;
>> +
>>   	if (!crypto_has_comp(zbackend->name, 0, 0)) {
>> -		pr_err("No %s compression\n", zbackend->name);
>> +		pr_err("Unknown compression: %s\n", zbackend->name);
>>   		return;
>>   	}
>>   
>> -	big_oops_buf_sz = zbackend->zbufsize(psinfo->bufsize);
>> -	if (big_oops_buf_sz <= 0)
>> +	size = zbackend->zbufsize(psinfo->bufsize);
>> +	if (size <= 0) {
>> +		pr_err("Invalid compression size for %s: %d\n",
>> +		       zbackend->name, size);
>>   		return;
>> +	}
>>   
>> -	big_oops_buf = kmalloc(big_oops_buf_sz, GFP_KERNEL);
>> -	if (!big_oops_buf) {
>> -		pr_err("allocate compression buffer error!\n");
>> +	buf = kmalloc(size, GFP_KERNEL);
>> +	if (!buf) {
>> +		pr_err("Failed %d byte compression buffer allocation for: %s\n",
>> +		       size, zbackend->name);
>>   		return;
>>   	}
>>   
>> -	tfm = crypto_alloc_comp(zbackend->name, 0, 0);
>> -	if (IS_ERR_OR_NULL(tfm)) {
>> -		kfree(big_oops_buf);
>> -		big_oops_buf = NULL;
>> -		pr_err("crypto_alloc_comp() failed!\n");
>> +	ctx = crypto_alloc_comp(zbackend->name, 0, 0);
>> +	if (IS_ERR_OR_NULL(ctx)) {
>> +		kfree(buf);
>> +		pr_err("crypto_alloc_comp('%s') failed: %ld\n", zbackend->name,
>> +		       PTR_ERR(ctx));
>>   		return;
>>   	}
>> +
>> +	/* A non-NULL big_oops_buf indicates compression is available. */
>> +	tfm = ctx;
>> +	big_oops_buf_sz = size;
>> +	big_oops_buf = buf;
>> +
>> +	pr_info("Using compression: %s\n", zbackend->name);
>>   }
>>   
>>   static void free_buf_for_compression(void)
>>   {
>> -	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && !IS_ERR_OR_NULL(tfm))
>> +	if (IS_ENABLED(CONFIG_PSTORE_COMPRESS) && tfm)
>>   		crypto_free_comp(tfm);
>>   	kfree(big_oops_buf);
>>   	big_oops_buf = NULL;
>> @@ -764,31 +784,28 @@ static void pstore_timefunc(struct timer_list *unused)
>>   			  jiffies + msecs_to_jiffies(pstore_update_ms));
>>   }
>>   
>> -void __init pstore_choose_compression(void)
>> +static int __init pstore_compression_late_init(void)
>>   {
>>   	const struct pstore_zbackend *step;
>>   
>>   	if (!compress)
>> -		return;
>> +		return 0;
>>   
>> +	/* Locate desired compression method. */
>>   	for (step = zbackends; step->name; step++) {
>>   		if (!strcmp(compress, step->name)) {
>>   			zbackend = step;
>> -			pr_info("using %s compression\n", zbackend->name);
>> -			return;
>> +			break;
>>   		}
>>   	}
>> -}
>>   
>> -static int __init pstore_compression_late_init(void)
>> -{
>>   	/*
>> -	 * Check if any pstore backends registered earlier but did not allocate
>> -	 * for compression because crypto was not ready, if so then initialize
>> -	 * compression.
>> +	 * Check if any pstore backends registered earlier but did not
>> +	 * initialize compression because crypto was not ready. If so,
>> +	 * then initialize compression now.
>>   	 */
>> -	if (psinfo && !tfm)
>> -		allocate_buf_for_compression();
>> +	allocate_buf_for_compression();
> 
> We can also get rid of the 'zbackend' global variable since choosing the
> compression backend and allocating the buffers are done at the same time?
> 
> Otherwise looks good to me,
> 
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 

Tested this on top of Joel's patch, works fine on getting early crash 
pstore dmesg logs, thanks.

Tested-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>

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